Promise.resolve()
    .then(value => new Promise((resolve, reject) => {
        setTimeout(() => {
            var a = 'hello'
            resolve(a)
        }, 10)
    }))
    .then(value => new Promise((resolve, reject) => {
        setTimeout(() => {
            var b = value + 'lagou'
            resolve(b)
        }, 10)
    }))
    .then(value => new Promise((resolve, reject) => {
        setTimeout(() => {
            var c = value + 'ILY'
            resolve(c)
        }, 10)
    }))
    .then(value => {
        console.log(value)
    })